The present invention relates to a liquid crystal display device, and to a separation method for forming each liquid crystal display panel from a mother board with a thinner glass substrate.
A liquid crystal display panel used for a liquid crystal display device includes: a TFT substrate in which pixels with pixel electrodes, thin film transistors (TFTs) and the like are arranged in a matrix; and a counter substrate in which color filters are formed at positions corresponding to the pixel electrodes. The counter substrate is disposed opposite the TFT substrate with a liquid crystal between the two substrates. The liquid crystal is sealed by a sealing material to bond the TFT substrate and the counter substrate together. Then, an image is formed by controlling the amount of light transmitted through the liquid crystal molecules for each pixel.
The liquid crystal display device, which can be made small and thin, is used in various applications such as mobile phone and digital still camera (DSC). In such a small liquid crystal display device, there is a growing demand for thinner liquid crystal display panels. The thickness of the liquid crystal display panel is most influenced by the thickness of the glass substrate, such as the TFT substrate or the counter substrate. Thus, it is necessary to reduce the thickness of the glass substrate in order to make the liquid crystal display panel thin.
The thickness of the glass substrate is standardized, for example, to 0.5 mm in the market. It is difficult to obtain a glass substrate other than the standardized one from the market. Further, a very thin substrate is poor in mechanical strength in the manufacturing process, which may be warped and difficult to flow on the production line.
Since the production of each liquid crystal display panel is not efficient, a method for forming multiple liquid crystal display panels in a mother board, and separating each liquid crystal display panel from the mother board is used. Then, the TFT substrate or counter substrate formed in the mother board is thinned by polishing the mother board in which a large number of liquid crystal display panels are formed.
In the liquid crystal display panel, there is a strong demand for a small profile of the liquid crystal display panel while keeping the display area unchanged, in addition to reducing the thickness of the liquid crystal display panel. To meet this requirement, Japanese Unexamined Patent Application Publication No. 2012-32506 describes a so-called a seal-portion cutting method. In this method, a seal portion is formed across a separation line of each liquid crystal display panel in a mother board, in which one seal portion is shared by adjacent liquid crystal display panels in the mother board. Then, the seal portion is separated for each liquid crystal display panel in the cutting process.
In this case, if the sealing material is present in the cut-out portion, it is difficult to separate the liquid crystal display panels from each other. Thus, Japanese Unexamined Patent Application Publication No. 2012-32506 describes a configuration to facilitate the separation of the individual liquid crystal display panels from the mother board, by forming a columnar spacer in the cut-out portion to reduce the amount of sealing material in the cut-out portion.